Many electronic devices, for example, FM radio receivers used for military purposes, presently include self-test arrangements. Typically, the self-test arrangement for an FM radio receiver includes an auxiliary oscillator that is connected to an r.f. front-end amplifier during a self-test operation. The oscillator is responsive to a modulator and control switches. The switches are connected to the modulator and oscillator to cause the modulator to be sequenced through a series of steps. In the first step, the oscillator supplies a constant frequency, unmodulated signal to the r.f. amplifier which drives i.f. circuitry, that in turn feeds a frequency detector that drives an audio frequency circuit. Responses from the i.f. and audio frequency circuits are derived and compared with reference values to determine the r.f. and noise characteristics of the receiver. Then, the oscillator is modulated to supply an FM modulated input to the r.f. amplifier. The audio frequency response is again derived under these circumstances and compared with a reference value to determine the receiver detection characteristics, as well as the center frequency and band width of the r.f. amplifier.
While the prior art arrangement functions satisfactorily, it has several disadvantages because of the substantial number of components which must be added. The additional components result in added cost, weight and size; they can also adversely affect reliability. The added weight and size have an adverse effect on portability, which is an important factor in many radio receivers, particularly military-type receivers.
It is, accordingly, and object of the present invention to provide a new and improved apparatus for and method of self-testing devices including amplifiers.
Another object of the invention is to provide a new and improved method and apparatus for self-testing devices including amplifiers, wherein relatively few additional components are needed for the self-test function.
Still another object of the invention is to provide a new and improved device having an amplifier and self-test capabilities, wherein the self testing is achieved with a very small number of added components.
A further object of the invention is to provide a relatively inexpensive, low-volume and low-weight arrangement for self-testing devices including an amplifier.